In vivo, vitamin D3 is first metabolized into 25-hydroxyvitamin D3 in the liver through hydroxylation at the 25-position, which in turn is metabolized into 1α, 25-dihydroxyvitamin D3 or 24R,25-dihydroxyvitamin D3 in the kidneys through hydroxylation at the 1α- or 24-position, respectively. Among these metabolites, 1α,25-dihydroxyvitamin D3 and its synthetic analogs are known to have a wide variety of physiological activities including calcium metabolism-regulatory activity, growth or differentiation-inhibitory activity against tumor cells or the like, and immunoregulatory activity.
Vitamin D3 has involved a problem that it would be likely to cause hypercalcemia when continuously used for a long period of time. To overcome this problem, attempts have been made to synthesize various vitamin D derivatives; there have been proposed some vitamin D derivatives that have a reduced hypercalcemic effect (e.g., JP 7-330714 A and JP 10-231284 A).
The object of the present invention is to provide vitamin D derivatives that have excellent physiological activities as medicines, particularly as therapeutic agents for skin diseases such as psoriasis, and that have a reduced hypercalcemic effect.